ADVANCED MATERIALS & PROCESSES | JULY 2026 24 Jewett and Halchak estimated the weight of alloy 718 in the space shuttle engine to be 51% contained in approximately 1500 separate parts[9]. These parts included high pressure turbo-pumps, tubing, valves, injectors, manifolds, nozzles, and innumerable fasteners. Manufacturing of rocket engine components has evolved dramatically in recent years with the development of powder based additive manufacturing techniques[10]. This technology has enabled the design of very complex parts with elaborate cooling structures, fewer welds and fasteners, and a more tightly controlled supply chain. The experience gained in this sector will continue to influence the design and manufacturing of alloy 718 on a much wider scale. OTHER CRYOGENIC AND POWER SYSTEMS The successful use of alloy 718 in rocket engines and the wealth of engineering data generated on high-field superconducting magnets by NASA for use in applications such as electric propulsion enabled its use in cryogenic applications that used liquid nitrogen or helium as a coolant[11,12]. High strength, ductility, and non-magnetic behavior allowed it to be substituted for high strength steels, initially at Argonne National Lab and later in dozens of research “cyclotrons” worldwide including the Large Hadron Collider. Alloy 718 is also used for structural supports and fasteners in medical devices including MRIs and CT scanners. At the extreme end of the size scale, alloy 718 is extensively utilized in the International Thermonuclear Energy Reactor an experimental fusion power station nearing completion at Cadarache in France[13]. Components include bolting, structural supports for the magnet system, first-wall blanket vacuum vessel, and bellows for the plasma divertor. This tokamak-style reactor or other fusion system designs partners developed the capability to produce finished alloy 718 turbine rotors weighing nearly 20,000 lbs (roughly ten times the weight of the largest aircraft rotors)[5]. A low carbon and niobium composition, triple melting, precise thermal management and incremental forging were key to this development. This manufacturing technology has since been leveraged to the production of shaft rotors for advanced energy systems that operate at higher temperatures than conventional ultra-supercritical steam and gas turbines, potentially expanding the use of alloy 718[6]. ROCKET ENGINES Shortly after filing the patent application, Inco introduced the still developmental alloy to NASA and rocket engine manufacturers. Liquid fueled rocket boosters were at that time being intensively developed for Earth orbit and ultimately lunar missions. While the combustion section of the rocket was an obvious place to use this new strong, weldable, heat-resistant alloy, it was also ideal for containment and pumping of liquid oxygen and hydrogen or organic fuels. Alloy 718 maintains its strength and toughness at cryogenic temperatures (-423°F/-253°C for liquid hydrogen). It replaced lower strength age- hardened iron-base alloys such as A-286 and cryogenic grades of austenitic stainless steel. Other age-hardened nickel-base alloys such as Waspaloy were susceptible to stress relief cracking that compromised weld joint integrity. The first use of alloy 718 was in 1966 for the injector back-plate fuel pump, second stage turbine disk and thrust chamber jacket in the Rocketdyne J-2 engine that powered the second and upper stages of the Saturn 1B and Saturn V launch vehicles[7]. The use of alloy 718 forgings and castings was expanded in later versions of the J-2 engine and in Aerojet General’s much larger M-1 engine system[8]. Alloy 718 may have reached its maximum volume in the Rocketdyne designed Space Shuttle Main Engine. At the 2nd Superalloy 718 Conference, The Rocketdyne J-2 engine, in operation from 1966-1975, is shown here during a test firing. Courtesy of Wikipedia. A cutaway drawing of the International Thermonuclear Energy Reactor, circa 2016. Courtesy of Wikimedia Commons.
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